/*
Copyright 2023 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package ini

// Copy from https://github.com/aws/aws-sdk-go
// May have been modified by Beijing Volcanoengine Technology Ltd.

import (
	"fmt"
	"io"
)

// State enums for the parse table
const (
	InvalidState = iota
	// StatementState stmt -> value stmt'
	StatementState
	// StatementPrimeState stmt' -> MarkComplete | op stmt
	StatementPrimeState
	// ValueState value -> number | string | boolean | quoted_string
	ValueState
	// OpenScopeState section -> [ section'
	OpenScopeState
	// SectionState section' -> value section_close
	SectionState
	// CloseScopeState section_close -> ]
	CloseScopeState
	// SkipState will skip (NL WS)+
	SkipState
	// SkipTokenState will skip any token and push the previous
	// state onto the stack.
	SkipTokenState
	// CommentState comment -> # comment' | ; comment'
	// comment' -> MarkComplete | value
	CommentState
	// MarkCompleteState MarkComplete state will complete statements and move that
	// to the completed AST list
	MarkCompleteState
	// TerminalState signifies that the tokens have been fully parsed
	TerminalState
)

// parseTable is a state machine to dictate the grammar above.
var parseTable = map[ASTKind]map[TokenType]int{
	ASTKindStart: {
		TokenLit:     StatementState,
		TokenSep:     OpenScopeState,
		TokenWS:      SkipTokenState,
		TokenNL:      SkipTokenState,
		TokenComment: CommentState,
		TokenNone:    TerminalState,
	},
	ASTKindCommentStatement: {
		TokenLit:     StatementState,
		TokenSep:     OpenScopeState,
		TokenWS:      SkipTokenState,
		TokenNL:      SkipTokenState,
		TokenComment: CommentState,
		TokenNone:    MarkCompleteState,
	},
	ASTKindExpr: {
		TokenOp:      StatementPrimeState,
		TokenLit:     ValueState,
		TokenSep:     OpenScopeState,
		TokenWS:      ValueState,
		TokenNL:      SkipState,
		TokenComment: CommentState,
		TokenNone:    MarkCompleteState,
	},
	ASTKindEqualExpr: {
		TokenLit: ValueState,
		TokenWS:  SkipTokenState,
		TokenNL:  SkipState,
	},
	ASTKindStatement: {
		TokenLit:     SectionState,
		TokenSep:     CloseScopeState,
		TokenWS:      SkipTokenState,
		TokenNL:      SkipTokenState,
		TokenComment: CommentState,
		TokenNone:    MarkCompleteState,
	},
	ASTKindExprStatement: {
		TokenLit:     ValueState,
		TokenSep:     OpenScopeState,
		TokenOp:      ValueState,
		TokenWS:      ValueState,
		TokenNL:      MarkCompleteState,
		TokenComment: CommentState,
		TokenNone:    TerminalState,
		TokenComma:   SkipState,
	},
	ASTKindSectionStatement: {
		TokenLit: SectionState,
		TokenOp:  SectionState,
		TokenSep: CloseScopeState,
		TokenWS:  SectionState,
		TokenNL:  SkipTokenState,
	},
	ASTKindCompletedSectionStatement: {
		TokenWS:      SkipTokenState,
		TokenNL:      SkipTokenState,
		TokenLit:     StatementState,
		TokenSep:     OpenScopeState,
		TokenComment: CommentState,
		TokenNone:    MarkCompleteState,
	},
	ASTKindSkipStatement: {
		TokenLit:     StatementState,
		TokenSep:     OpenScopeState,
		TokenWS:      SkipTokenState,
		TokenNL:      SkipTokenState,
		TokenComment: CommentState,
		TokenNone:    TerminalState,
	},
}

// ParseAST will parse input from an io.Reader using
// an LL(1) parser.
func ParseAST(r io.Reader) ([]AST, error) {
	lexer := iniLexer{}
	tokens, err := lexer.Tokenize(r)
	if err != nil {
		return []AST{}, err
	}

	return parse(tokens)
}

// ParseASTBytes will parse input from a byte slice using
// an LL(1) parser.
func ParseASTBytes(b []byte) ([]AST, error) {
	lexer := iniLexer{}
	tokens, err := lexer.tokenize(b)
	if err != nil {
		return []AST{}, err
	}

	return parse(tokens)
}

func parse(tokens []Token) ([]AST, error) {
	start := Start
	stack := newParseStack(3, len(tokens))

	stack.Push(start)
	s := newSkipper()

loop:
	for stack.Len() > 0 {
		k := stack.Pop()

		var tok Token
		if len(tokens) == 0 {
			// this occurs when all the tokens have been processed
			// but reduction of what's left on the stack needs to
			// occur.
			tok = emptyToken
		} else {
			tok = tokens[0]
		}

		step := parseTable[k.Kind][tok.Type()]
		if s.ShouldSkip(tok) {
			// being in a skip state with no tokens will break out of
			// the parse loop since there is nothing left to process.
			if len(tokens) == 0 {
				break loop
			}

			step = SkipTokenState
		}

		switch step {
		case TerminalState:
			// Finished parsing. Push what should be the last
			// statement to the stack. If there is anything left
			// on the stack, an error in parsing has occurred.
			if k.Kind != ASTKindStart {
				stack.MarkComplete(k)
			}
			break loop
		case SkipTokenState:
			// When skipping a token, the previous state was popped off the stack.
			// To maintain the correct state, the previous state will be pushed
			// onto the stack.
			stack.Push(k)
		case StatementState:
			if k.Kind != ASTKindStart {
				stack.MarkComplete(k)
			}
			expr := newExpression(tok)
			stack.Push(expr)
		case StatementPrimeState:
			if tok.Type() != TokenOp {
				stack.MarkComplete(k)
				continue
			}

			if k.Kind != ASTKindExpr {
				return nil, NewParseError(
					fmt.Sprintf("invalid expression: expected Expr type, but found %T type", k),
				)
			}

			k = trimSpaces(k)
			expr := newEqualExpr(k, tok)
			stack.Push(expr)
		case ValueState:
			// ValueState requires the previous state to either be an equal expression
			// or an expression statement.
			//
			// This grammar occurs when the RHS is a number, word, or quoted string.
			// equal_expr -> lit op equal_expr'
			// equal_expr' -> number | string | quoted_string
			// quoted_string -> " quoted_string'
			// quoted_string' -> string quoted_string_end
			// quoted_string_end -> "
			//
			// otherwise
			// expr_stmt -> equal_expr (expr_stmt')*
			// expr_stmt' -> ws S | op S | MarkComplete
			// S -> equal_expr' expr_stmt'
			switch k.Kind {
			case ASTKindEqualExpr:
				// assiging a value to some key
				k.AppendChild(newExpression(tok))
				stack.Push(newExprStatement(k))
			case ASTKindExpr:
				k.Root.raw = append(k.Root.raw, tok.Raw()...)
				stack.Push(k)
			case ASTKindExprStatement:
				root := k.GetRoot()
				children := root.GetChildren()
				if len(children) == 0 {
					return nil, NewParseError(
						fmt.Sprintf("invalid expression: AST contains no children %s", k.Kind),
					)
				}

				rhs := children[len(children)-1]

				if rhs.Root.ValueType != QuotedStringType {
					rhs.Root.ValueType = StringType
					rhs.Root.raw = append(rhs.Root.raw, tok.Raw()...)

				}

				children[len(children)-1] = rhs
				k.SetChildren(children)

				stack.Push(k)
			}
		case OpenScopeState:
			if !runeCompare(tok.Raw(), openBrace) {
				return nil, NewParseError("expected '['")
			}

			stmt := newStatement()
			stack.Push(stmt)
		case CloseScopeState:
			if !runeCompare(tok.Raw(), closeBrace) {
				return nil, NewParseError("expected ']'")
			}

			k = trimSpaces(k)
			stack.Push(newCompletedSectionStatement(k))
		case SectionState:
			var stmt AST

			switch k.Kind {
			case ASTKindStatement:
				// If there are multiple literals inside of a scope declaration,
				// then the current token's raw value will be appended to the Name.
				//
				// This handles cases like [ profile default ]
				//
				// k will represent a SectionStatement with the children representing
				// the label of the section
				stmt = newSectionStatement(tok)
			case ASTKindSectionStatement:
				k.Root.raw = append(k.Root.raw, tok.Raw()...)
				stmt = k
			default:
				return nil, NewParseError(
					fmt.Sprintf("invalid statement: expected statement: %v", k.Kind),
				)
			}

			stack.Push(stmt)
		case MarkCompleteState:
			if k.Kind != ASTKindStart {
				stack.MarkComplete(k)
			}

			if stack.Len() == 0 {
				stack.Push(start)
			}
		case SkipState:
			stack.Push(newSkipStatement(k))
			s.Skip()
		case CommentState:
			if k.Kind == ASTKindStart {
				stack.Push(k)
			} else {
				stack.MarkComplete(k)
			}

			stmt := newCommentStatement(tok)
			stack.Push(stmt)
		default:
			return nil, NewParseError(
				fmt.Sprintf("invalid state with ASTKind %v and TokenType %v",
					k, tok.Type()))
		}

		if len(tokens) > 0 {
			tokens = tokens[1:]
		}
	}

	// this occurs when a statement has not been completed
	if stack.top > 1 {
		return nil, NewParseError(fmt.Sprintf("incomplete ini expression"))
	}

	// returns a sublist which excludes the start symbol
	return stack.List(), nil
}

// trimSpaces will trim spaces on the left and right hand side of
// the literal.
func trimSpaces(k AST) AST {
	// trim left hand side of spaces
	for i := 0; i < len(k.Root.raw); i++ {
		if !isWhitespace(k.Root.raw[i]) {
			break
		}

		k.Root.raw = k.Root.raw[1:]
		i--
	}

	// trim right hand side of spaces
	for i := len(k.Root.raw) - 1; i >= 0; i-- {
		if !isWhitespace(k.Root.raw[i]) {
			break
		}

		k.Root.raw = k.Root.raw[:len(k.Root.raw)-1]
	}

	return k
}
